1. Field of the Invention
The present invention relates to a backlighting panel for an LCD module. More particularly, the invention relates to an LED backlighting panel for an LCD module.
2. Description of the Prior Art
Heretofore various backlighting panels have been proposed. Several of these panels are disclosed in the following U.S. Patents:
______________________________________ U.S. Pat. No. PATENTEE ______________________________________ 3,864,905 Richardson 3,869,195 Aldrich et al 3,881,809 Fergason et al 3,994,564 Somogyi 4,017,155 Yagi et al 4,042,294 Billings, Jr. et al 4,043,636 Eberhardt et al 4,088,992 Kmetz et al 4,126,383 Doriguzzi et al 4,196,581 Nemoto ______________________________________
The Richardson U.S. Pat. No. 3,864,905 discloses a liquid crystal horological instrument employing a display comprising a layer of liquid crystal material sandwiched between two transparent parallel plates and incorporating a reflective surface on the side of the display opposite the side which is viewed by the observer. In the absence of ambient light, the display is illuminated by an electric lamp incorporated in the instrument.
The Aldrich et al U.S. Pat. No. 3,869,195 discloses a liquid crystal display containing a segmented source of backlighting, such source comprising a continuous electroluminescent panel sandwiched between transparent electrodes with at least one of the electrodes being segmented to provide high brightness and contrast over a wide range of ambient lighting conditions.
The Fergason U.S. Pat. No. 3,881,908 discloses a reflection system for liquid crystal displays for high efficiency reflection without ghosts or background images. This is accomplished by the use of an LCD of the polarized light shutter type and by the use of a diffuse reflector placed behind a polarized liquid crystal cell. The reflector scatters the light at very large angles to provide a good viewing range while preserving polarization. The result is a gain in contrast lighting.
The Somogyi U.S. Pat. No. 3,994,564 discloses a light pipe reflector for use in a liquid crystal or other display wherein a light pipe formed of optically clear material having a clear, lightly etched, top surface and patterned bottom surface are utilized. An enlarged portion is provided at one edge and contains a cavity for insertion of a light bulb. The light pipe is covered with a highly reflective coating except for the clear top surface and the interior portion of the cavity.
The Yagi et al U.S. Pat. No. 4,017,155 discloses a liquid crystal display device which is very thin and suitable for wrist watches. It comprises upper and lower transparent plates having the liquid crystal material sandwiched therebetween. A reflective plate having a roughened upper surface is disposed beneath the lower transparent plate with the roughened surface facing the lower transparent plate. A light source is located alongside one side edge of the reflective plate and coacts with a light-reflecting hood encasing the display panel. By locating the light source along the side of the reflecting plate and by employing the light reflecting hood, the display device may be made very thin.
The Billings, Jr. et al U.S. Pat. No. 4,042,294 discloses an electro-optical display system including front and rear optically transmissive panels that are spaced apart in substantially parallel configuration. A liquid crystal composition in disposed between the panels and optically transmissive electrodes are disposed on the opposing surfaces of the front and rear panels. The electrodes are attached to electrical leads whereby a voltage can be impressed between selected front and rear electrodes to illuminate the panel, the light source being a luminous radioactive panel or light pipe plate with at least one light source adjacent an edge of the light pipe plate.
The Eberhardt et al U.S. Pat. No. 4,043,636 discloses an illumination panel for the enhancement of brightness of a liquid crystal display for a watch or similar device. The panel has an internal light source which has a suitable shape and a reflectorized coating to direct internal and external light in the desired direction. More particularly, a transparent layer or member with an internal light source is mounted at one end and selectively coated with a metallic reflective material to reflect light from internal and external sources through a cross-hatched surface or a matte finished window on the surface of the member, which is mounted adjacent to the exterior surface of the bottom substrate of the display. Diffused light is transmitted from the internal light source through the bottom substrate of the display.
The Kmetz et al U.S. Pat. No. 4,088,992 discloses an electro-optical display device including a liquid crystal cell arranged between two polarizers. A light source such as an LED is positioned adjacent one polarizer on the side thereof remote from the liquid crystal cell and an electronic control device is coupled to the liquid crystal cell. A diaphragm is arranged on one side of the liquid crystal cell to form an aperture for limiting the display field of the liquid crystal to limit viewing parallex and to improve contrast.
The Doriguzzi et al U.S. Pat. No. 4,126,383 discloses an electro-optic display device which can be operated in either the transmissive or reflective mode. The device consists of a liquid crystal display cell and a semitransparent reflector located on or in a circuit board having a light emitting element such as a miniature bulb and having at least one light conducting region.
The Nemoto U.S. Pat. No. 4,196,581 discloses a liquid crystal display electronic wristwatch having a lamp therein to illuminate the liquid crystal display mounted in the watch case beneath a display panel so as to overlap with the display.
As will be described in detail below, the backlighting panel of the present invention differs from the previously proposed backlighting panels by providing a panel having a light diffusing surface and light emitting means on two opposite sides thereof. In this way the panel can be illuminated from the edges thereof by a number of direct current powered LED's which require only a small amount of power. The power consumption of the panel will then be lower than the power required for electroluminescent panels which require a high alternating current power supply or additional circuitry for converting direct current to alternating current.
A further decrease in power consumption may be achieved by adjusting the duty cycle of the direct current to the LED's to a frequency which is not detectable by the human eye.